Reducing the amount of energy consumed by a machine for cleansing articles, such as a clothes washer, is a significant problem, in part because of increasing energy costs. In such a machine, the amount of energy consumed is primarily determined by the amount of energy needed to heat the liquid, such as water, used to cleanse the articles. Thus, decreased liquid consumption for such machines may result in a significant improvement in energy efficiency.
Appliances for cleansing articles, such as clothes washers, are typically preprogrammed to perform a complete washing in a predetermined number of wash cycles, each wash cycle having a predetermined duration. A wash cycle may comprise providing substantially particle-free liquid to the machine, circulating the liquid during the wash cycle, and draining or flushing the liquid from the machine after being used to wash or cleanse the articles. Often the machine user may select from a limited number of preprogrammed options. Such preprogramming does not use energy efficiently because the machine may either perform an excessive number of wash cycles, or perform each cycle for an excessive duration, to assure that cleanliness of the articles is achieved. To improve the energy efficiency of such appliances, closed loop feedback control has been introduced. Several techniques are available to indirectly monitor cleanliness of the articles during closed loop feedback control of the appliance, including use of a device for measuring the turbidity of the liquid used to wash the articles.
Devices for measuring turbidity that detect the transmission of light propagated through water used to wash the articles have been employed to ascertain information about progress of the wash. However, these devices are not ideal for use in household appliances. Such devices are oftentimes difficult or non-economic to implement due to the electronic circuitry necessary to perform the complex turbidity measurements. Furthermore, such devices are subject to measurement error. Factors such as water turbulence, cloudiness of the water sample chamber, light source dimming, or device performance degradation may cause attenuation of the amount of light detected and thus affect measurement accuracy. The precision of such devices is also not entirely satisfactory. This imprecision has the additional effect of making turbidity measurements provided by such devices difficult to interpret in a closed loop feedback control system.
A need thus exists for a machine for cleansing articles incorporating a device for measuring turbidity in which the device is simple and economic to produce, provides the capability to compensate for signal attenuation, and provides improved turbidity measurement precision. A need also exists for a closed loop feedback control system sophisticated enough to utilize the measurements from such a turbidity measuring device effectively.